CN114952182B - Internal thread step-by-step cold extrusion process - Google Patents
Internal thread step-by-step cold extrusion process Download PDFInfo
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Abstract
According to the internal thread step-by-step cold extrusion process, the diameter formula of the bottom hole in the internal thread cold extrusion process is calculated, so that the quality of a workpiece is ensured; the step-by-step cold extrusion is carried out, so that the torque in the extrusion process is greatly reduced, the wear speed of the tap is greatly reduced, the process cost is reduced, the roughness of the internal thread can be reduced by step-by-step extrusion, the residual stress and the hardening layer in each extrusion process are reserved, and the fatigue strength and the service life of a workpiece are improved.
Description
Technical Field
The invention relates to a stepwise cold extrusion process for internal threads.
Background
With the development of high performance, low cost and low energy consumption of internal thread processing, the cold extrusion forming process becomes an important component for improving the mechanical performance of the internal thread and solving the problem of residual metal chips of the internal thread of the blind hole, and has wide application prospect in the fields of aviation, aerospace, high-speed trains, important mechanical engineering and the like.
The cold extrusion of the internal thread has high thread accuracy and good surface integrity due to the forming of the internal thread, and the cold work hardening state of the surface and the secondary surface of the internal thread after the cold extrusion is maintained, so that the thread connection strength and the fatigue resistance life of the internal thread are improved.
The cold extrusion forming process of the internal thread is to adopt a cold extrusion tap to make metal generate plastic flow on a preset workpiece bottom hole under the room temperature condition through the extrusion action of the edge teeth, so as to form the internal thread.
Compared with cutting forming of internal threads, cold extrusion forming of internal threads has the following advantages:
(1) the screw thread cold extrusion forming process belongs to elastoplastic deformation, and due to the good guiding property of the extrusion screw tap, the forming screw thread has small forming error, and the common materials can reach the processing precision of 4H or 5H.
(2) The surface roughness is low, the edge teeth of the extrusion tap part are very flat to the internal thread tooth surfaces in the cold extrusion forming process of the internal thread, and the surface roughness can reach Ra0.4-Ra0.8.
(3) The tensile strength and the fatigue resistance are improved, and the internal thread extrusion is a process of filling the whole tooth form by plastic deformation of metal to enable the metal to generate plastic flow. Therefore, the formed thread surface tissue is fibrillated and distributed along the tooth shape, and a work hardening layer and residual stress exist on the thread root and the tooth flank, so that the tensile strength and the fatigue resistance of the thread are greatly improved.
(4) Because no internal thread is machined by cutting, no residual metal scraps exist in the internal thread, and short-circuit accidents of electrical elements caused by the metal scraps can be avoided for the blind hole internal thread.
The cold extrusion internal thread is not widely used in aerospace, and only a cold extrusion process is adopted for extruding the blind hole internal thread product with M less than or equal to 2. And the yield strength sigma s is less than or equal to 250mPa at low hardness; the material is used. The reasons for this are not generally adopted are as follows:
(1) the cold extrusion internal thread process has the advantages of improving the fatigue strength of products, improving the precision of workpieces, reducing the roughness, having no metal chips in blind hole internal threads and the like.
(2) The bottom aperture of the internal thread is cold extruded, and a suitable and practical calculation method cannot be found.
(3) The size of the bore diameter of the internal thread bottom directly influences the tooth high rate (small diameter size) and the cold extrusion torque. Large aperture, small tooth height rate and unqualified products. The aperture is small, the tooth high rate is qualified, but the torque is large, the screw tap is easy to wear, and the screw tap is easy to break and cannot be processed. This is a major reason for restricting the widespread use of cold extrusion.
Disclosure of Invention
In order to solve the technical problems, the invention provides a stepped cold extrusion process for internal threads.
The invention is realized by the following technical scheme.
The invention provides a step-by-step cold extrusion process for internal threads, which comprises the following steps:
s1, calculating a functional relation between the diameter of a bottom hole and the nominal diameter and the screw pitch of an internal thread of a workpiece;
in the process of extruding the screw tap into the workpiece, the volume V2 of the screw thread metal extruded by the screw tap is equal to the volume V1 of the screw thread groove generated by extruding the screw thread extrusion edge tooth into the inner wall of the workpiece,
V 1 ＝V 2 (1)
V 1 ＝2π×〔(h 1 /3×(2a 1 ﹢b 1 )/(a 1 ﹢b 1 ))﹢d 0 /2〕×(a 1 ﹢b 1 )
/2×h 1 (2)
V 2 ＝2π×〔(h 2 /3×(2a 2 ﹢b 2 )/(a 2 ﹢b 2 ))﹢d 1 /2〕×(a 2 ﹢b 2 )
/2×h 2 (3)
a 1 ＝0.125P (4)，
b 1 ＝0.125P﹢0.5774(d﹣d0) (5)，
a 2 ＝0.875P﹣0.5774(d﹣d0) (6)，
b 2 ＝0.25P (7)，
h 1 ＝(d﹣d 0 )/2 (8)，
h 2 ＝(d 0 ﹣d 1 )/2 (9)，
d 1 ＝d﹣1.0825P (10)，
b 1 ﹢a 2 ＝P (11)
bringing formulae (2) - (11) into formula (1) to give d 0 ≈d-0.60P。
S2, correcting the diameter d of the bottom hole according to the numerical value of the thread tolerance zone 0 ＝d﹣(0.43～0.60)P，
Wherein a is 1 Is the width of the thread crest of the thread groove, b 2 Crest width, h, of thread extruded for tap 1 Depth of screw tap into thread groove, h 2 The thread height of the extrusion thread for the tap, P is the pitch, d 1 The diameter of the thread is small, and d is the nominal diameter of the internal thread of the workpiece;
s3, selecting the diameter of the bottom hole according to the workpiece material and then machining the bottom hole;
s4, performing cold extrusion processing on the internal threads of the workpiece step by using the screw tap.
The distribution processing steps are as follows:
s41, performing primary cold extrusion on the internal thread of the workpiece by using a small-diameter tap with the diameter smaller than the nominal diameter of the internal thread of the workpiece and the screw pitch identical to that of the internal thread of the workpiece, so that the displacement volume of the metal on the inner wall of the workpiece is a complete internal thread displacement volume V 1 64% -75% of the total weight of the steel sheet;
s42, performing one-time cold extrusion by using a standard tap with the diameter equal to the nominal diameter of the internal thread of the workpiece and the screw pitch identical to that of the internal thread of the workpiece to obtain the complete internal thread.
The rotating speed of the machine tool in the steps S41 and S42 is 25r/min, and cold extrusion special oil is used in the extrusion process.
The diameter of the small-diameter tap in the S41 is calculated by the following method:
V3＝(64％～75％)V1 (12)，
V3＝2π×〔(h 3 /3×(2a 3 ﹢b 3 )/(a 3 ﹢b 3 ))﹢d 0 /2〕×(a 3 ﹢b 3 )
/2×h 3 (13)，
h 3 ＝(d 3 ﹣d 0 )/2 (14)，
a 3 ＝0.125P (15)，
b 3 ＝0.125P﹢0.5774(d 3 ﹣d 0 ) (16)，
carrying out the following steps (2), (13) to (16) into formula (12)
d 3 ＝d－(0.1～0.15)P。
V3 is the volume of the small-diameter screw tap extruded into the thread groove, a 3 The crest width h of the thread groove is extruded into the tap with small diameter 3 D, the depth of the small-diameter tap extruded into the thread groove 3 Is the nominal diameter of the small diameter tap.
And if the bottom hole of the workpiece is a through hole, carrying out step-by-step processing by using a combined tap.
The combined tap comprises a small-diameter section and a standard section, wherein the small-diameter section and the standard section are connected smoothly through a transition section, the other end of the small-diameter section is connected with a positioning head smoothly, and the other end of the standard section is connected with a clamping handle.
The diameter of the small diameter section is the diameter relation of the standard section: d, d Small size ＝d Label (C) ﹣(0.1～0.15)P。
The clamping handle is a thick handle or a thin handle.
The diameter of the clamping handle of the thick handle is larger than that of the standard section, and the clamping handle is smoothly connected with the standard section.
The diameter of the clamping handle of the thin handle is smaller than that of the standard section.
The invention has the beneficial effects that:
1. and the quality of the workpiece is ensured by calculating a diameter formula of the bottom hole in the cold extrusion process of the internal thread.
2. The extrusion process is divided into two times of extrusion, so that the torque in the extrusion process is greatly reduced, the wear speed of the tap is greatly reduced, and the production cost is reduced;
3. the roughness of the internal thread can be reduced by step extrusion, the residual stress and the hardening layer in each extrusion process are reserved, and the fatigue strength and the service life of the workpiece are improved.
Drawings
FIG. 1 is a schematic view of a thread form construction of the present invention;
FIG. 2 is a torque schematic of the internal thread extrusion process of the present invention;
FIG. 3 is a graph of tooth height versus thread connection strength for the present invention;
FIG. 4 is a plot of bottom hole diameter versus extrusion torque for the present invention;
FIG. 5 is a schematic view of the rough stem combination extrusion tap of the invention;
FIG. 6 is a schematic view of the construction of a thin shank combination tap of the invention;
FIG. 7 is a schematic cross-sectional view of the processing section of the tap of the invention;
FIG. 8 is a schematic cross-sectional view of the tap holder shank of the invention;
FIG. 9 is a profile of the present invention formed by step extrusion of M3 threads;
1-small diameter section, 2-transition section, 3-standard section, 4-clamping handle and 5-positioning head.
Detailed Description
The technical solution of the present invention is further described below, but the scope of the claimed invention is not limited to the above.
An internal thread step-by-step cold extrusion process comprises the following steps:
s1, calculating a functional relation between the diameter of a bottom hole and the nominal diameter and the screw pitch of a screw thread;
in the process of extruding the screw tap into the workpiece, the volume V2 of the screw thread metal extruded by the screw tap is equal to the volume V1 of the screw thread groove generated by extruding the screw thread extrusion edge tooth into the inner wall of the workpiece,
V 1 ＝V 2 (1)
V 1 ＝2π×〔(h 1 /3×(2a 1 ﹢b 1 )/(a 1 ﹢b 1 ))﹢d 0 /2〕×(a 1 ﹢b 1 )
/2×h 1 (2)
V2＝2π×〔(h 2 /3×(2a 2 ﹢b 2 )/(a 2 ﹢b 2 ))﹢d 1 /2〕×(a 2 ﹢b 2 )
/2×h 2 (3)
a 1 ＝0.125P (4)，
b 1 ＝0.125P﹢0.5774(d﹣d 0 ) (5)，
a 2 ＝0.875P﹣0.5774(d﹣d 0 ) (6)，
b 2 ＝0.25P (7)，
h 1 ＝(d﹣d 0 )/2 (8)，
h 2 ＝(d 0 ﹣d 1 )/2 (9)，
d 1 ＝d﹣1.0825P (10)
b 1 ﹢a 2 ＝P (11)
bringing formulae (2) - (11) into formula (1) to give d 0 ≈d-0.60P。
S2, correcting the diameter d of the bottom hole according to the numerical value of the thread tolerance zone 0 ＝d﹣(0.43～0.60)P，
Wherein a is 1 Is the width of the thread crest of the thread groove, b 2 Crest width, h, of thread extruded for tap 1 Depth of screw tap into thread groove, h 2 The thread height of the extrusion thread for the tap, P is the pitch, d 1 The diameter of the thread is small, and d is the nominal diameter of the internal thread of the workpiece;
s3, selecting the diameter of the bottom hole according to the workpiece material and then machining the bottom hole;
s4, performing cold extrusion processing on the internal threads of the workpiece step by using the screw tap.
The step-by-step processing steps are as follows:
s41, performing primary cold extrusion on the internal thread of the workpiece by using a small-diameter screw tap with the diameter smaller than the nominal diameter of the internal thread of the workpiece and the screw pitch identical to that of the internal thread of the workpiece,the displacement volume of the metal on the inner wall of the workpiece is the complete internal thread displacement volume V 1 64% -75% of the total weight of the steel sheet;
s42, performing one-time cold extrusion by using a standard tap with the diameter equal to the nominal diameter of the internal thread of the workpiece and the screw pitch identical to that of the internal thread of the workpiece to obtain the complete internal thread.
The machine tool rotational speed in the steps S41 and S42 is 25r/min.
The diameter of the small-diameter tap in the S41 is calculated by the following method:
V 3 ＝(64％～75％)V 1 (12)，
V 3 ＝2π×〔(h 3 /3×(2a 3 ﹢b 3 )/(a 3 ﹢b 3 ))﹢d 0 /2〕×(a 3 ﹢b 3 )
/2×h 3 (13)，
h 3 ＝(d 3 ﹣d 0 )/2 (14)，
a 3 ＝0.125P (15)，
b 3 ＝0.125P﹢0.5774(d 3 ﹣d 0 ) (16)，
bringing (2), (13) to (16) into (11)
d 3 ＝d－(0.1～0.15)P。
V 3 A is the volume of the small diameter tap extruded into the thread groove 3 The crest width h of the thread groove is extruded into the tap with small diameter 3 D, the depth of the small-diameter tap extruded into the thread groove 3 Is the nominal diameter of the small diameter tap.
And if the bottom hole of the workpiece is a through hole, carrying out step-by-step processing by using a combined tap.
Example 1: the invention finds the easy fracture reason of the tap in the cold extrusion process of the internal thread,
as shown in fig. 2, cold extrusion of internal threads can be divided into three main stages:
a) an extrusion stage, b) an extrusion and correction simultaneous stage, c) a correction stage torque at each stage.
Tap material: there are W18WCr4V, W M05Cr4V2Al, W7Mo4CrV2Co5 high speed steels, and cemented carbides. High-speed steel, hard alloy and other materials are coated. A TiN and TiALN coating;
judging the strength of the tap:
τ max ＝Mnmax/Wn≤〔τ〕 ， τ max maximum working shear stress.
[ tau ] is provided: allowable stress of material, M n Torque, wn: torsional section modulus.
Torsional section modulus of tap W n ＝πD 3 And/16, D, the tap diameter is small. If D is small, τ max And the tap is easy to break due to the fact that the tap is more than [ tau ]. This is why particularly small taps are prone to breakage. The hardness HRC of the workpiece material is more than 25, cold extrusion is very difficult, such as M2 threads, the hardness of the material 022Cr19Ni5MO3Si2N is more than HRC30, the torque is particularly large, and tap breakage is very large. Alloy extrusion tap is large in brittleness, easy to brittle fracture and tooth breakage, and has inferior service performance (effect) as high-speed steel extrusion tap.
Example 2: analyzing the relationship between thread high rate and thread connection strength
Analyzing factors influencing torque in the production process:
1. the lubricant, the rotational speed of the lathe (drilling machine), the general lubricant adopts the special oil of extrusion, its coefficient of friction is smaller;
2. rotational speed of machine tool (drilling machine), based on yield strength sigma of material s HRC size is determined and typically controlled at a lower rotational speed.
3. The largest factor influencing the torque is the diameter of the reserved thread bottom hole, the diameter of the bottom hole is small, and the tooth height rate is large. The high rate of the general teeth can be controlled to be more than 70 percent.
As shown in fig. 3, after the tooth height rate exceeds 70%, the connection strength of the threads is not significantly increased, and the required compression torque is significantly increased.
The high rate of the thread of the internal thread increases with the diameter of the bottom hole of the workpiece in the cold extrusion forming process of the internal thread. Generally, high tooth rates, i.e., small box diameters, are not necessarily required to meet internal thread connection strength. The small diameter of the workpiece is required to be qualified in the production. However, if HRC > 25 or σs > 450mPa and the screw plug gauge (T, Z) is ensured to be closed and the small diameter d1 is qualified, the extrusion tap cannot ensure certain yield. For example, M2 and 022Cr19Ni5MO3Si2N (HRC 30), one tap can only process 2-5 parts, the cost is high, cold extrusion internal thread processing cannot be adopted, the hardness of a high-temperature alloy and a stainless steel material used by aerospace enterprises is more than 30, and the hardness of a titanium alloy material is more than 30. If the internal threads are cold extruded, the torque can be excessive, and the tap wears and even breaks. The bottom hole diameter size is very sensitive to torque. Cold extrusion internal thread processing method is not adopted.
Example 3, bottom hole diameter was analyzed as a function of torque.
As shown in fig. 1, taking a common thread as an example, the volume of the rotating body at A1 in the drawing is:
V 1 ＝2π×〔(h 1 /3×(2a 1 ﹢b 1 )/(a 1 ﹢b 1 ))﹢d 0 /2〕×(a 1 ﹢b 1 )
/2×h 1 ，
wherein h is 1 ＝(d﹣d 0 )/2，
a 1 ＝0.125P，
b 1 ＝0.125P﹢0.5774(d﹣d 0 )，
h 1 ＝(d﹣d 0 )/2，
Wherein a is 1 Is the width of the thread crest of the thread groove, h 1 The depth of the screw tap extruded into the thread groove is P is the screw pitch, d 1 Is a small diameter of the thread.
Handle a 1 ，b 1 ，h 1 Carrying out formula solving, and obtaining:
V 1 ＝a(d﹣d 0 ) 3 ﹢b(d﹣d 0 ) 2 ﹢C(d﹣d 0 ). Wherein a, b, c > 0.a, a
＝0.048125π、b＝(0.3125P﹢0.14435d 0 )π、c＝0.0625πPd 0 ，V 1 Is (d-d) 0 ) And adding a function. Let x=d-d 0 The volume change formula of the A1 rotator is dV 1 ＝(3aX 2 2 bX+C) dx, it is known that dV1 changes due to volumeChemical and (d-d) 0 ) There is a very sensitive relationship. V1=f (x) is a nonlinear function. This is the cold extrusion internal thread deformation (V and d 0 ) Is an important feature of (a).
The metal deformation, plasticity and deformation resistance are related to the degree of deformation of the displacement volume, the displacement volume of the cold extrusion screw thread is related to the third power, the second power and the first power of (d-d 0) as the deformation of the displacement volume increases, and the displacement volume is related to the deformation displacement. Description of internal thread extrusion volume Change dv= (3 aX 2 The characteristic of the + < 2bX >) dx nonlinear relationship is the most important factor restricting the wide use of cold-extruded internal threads ≡! The diameter of the reserved bottom hole is controlled inaccurately, the precision is insufficient, and the workpiece tooth shape, the tooth height rate, T, Z and the small-diameter size qualification rate are directly affected. Affecting residual stress, mechanical properties, fatigue life, etc. The extrusion tap is affected to adhere to the workpiece, and the abrasion degree is even broken in the internal thread bottom hole. Therefore, the cold extrusion internal thread processing, the material and the hardness are all strictly limited, and the thread diameter is strictly limited.
Establishing a mechanical model of the cold extrusion forming process of the internal thread, analyzing stress conditions, contact angles and contact arc lengths of each stage, and calculating torque of each stage:
depending on the working portion structure of the extrusion tap, the internal thread cold extrusion process can be divided into three main stages: 1 extrusion stage, 2 extrusion and correction simultaneously, and 3 correction stage, and the torque of each stage is shown in fig. 2. The torque change trend in the whole internal thread cold extrusion forming process is as follows: in the stage I, the extruding tap edge teeth continuously extrude the workpiece, the metal plastic deformation of the workpiece continuously occurs, and the torque in the whole stage is continuously increased; in the II stage, the extrusion effect and the correction effect exist simultaneously, and the torque in the stage is increased and then reduced; in stage III, as the extrusion tap is guided out, the edge teeth of the extrusion tap involved in correction are continuously reduced, and the torque value is continuously reduced. The maximum value of the torque in the forming process can be used as an index for calibrating the torque in the whole forming process.
The torque maximum value calculation formula in the cited internal thread extrusion process is as follows:
T＝3.92×10 -4 σ s H V m 0.8783 n 0.014 L1 0.2718 L2 0.6298 φ 0.05 K -1.396 z 0.1039 (d－d 0 ) 2 P
wherein sigma s is the yield stress (MPa) of the extruded workpiece material, HV is the Vickers hardness of the material; m is the average friction coefficient between the extrusion tap and the workpiece; n is the rotating speed (r/min) of the machine tool; d0 is the diameter (mm) of a bottom hole of the prefabricated workpiece; l1 is the length (mm) of the extrusion tap part; l2 is the correction part length (mm); phi is the extrusion cone angle (°); k is the back-off amount (mm); z is the number of teeth; d is the large-diameter nominal diameter (mm) of the extrusion tap; p is the extrusion tap pitch (mm).
From this equation it can be seen that the torque T is mainly proportional to the workpiece material σs, HV, indicating that the harder the material the greater the torque, the greater the yield hardness and the greater the torque. The friction coefficient (m) is related, but the degree of influence is not σs, HV is large, and is known from the function of T. Most important is T and (d-d) 0 ) 2 In relation, t=k (d-d) 0 ) 2 Nonlinear is a square relationship.
And (3) calculating according to test data by using a mathematical least square method: t=398.1× (22-d) 0 ) 2.28 The calculated and tested relative errors are shown in Table 1.
Table 1 t=398.1× (22-d) 0 ) 2.28 Calculation results and test results comparison table
And (3) calculating according to test data by using a mathematical least square method: t=39.8× (8-d) 0 ) 3.35 Its meter
The calculation and test relative errors are shown in Table 2.
Table 2 at t=39.8× (8-d) 0 ) 3.35 Calculation results and test results comparison table
From the experimental results, the torque t=k (d-d) 0 ) 2～4 And K > 0 is a constant since the material chemistry, texture, σs, HV, tap size, coefficient of friction, etc. parameters are unchanged during product processing.
Example 4, bottom hole diameter minima were calculated.
As shown in FIG. 1, triangle OAB is similar to triangle OCD in the figure, since a 1 =0.125P, so b 1 ＝0.125P﹢0.5774(d﹣d 0 )，
Triangle MFG is similar to triangle MDE, since b 2 =0.25P, so a 2 ＝0.875P﹣0.5774(d﹣d 0 ) And b 1 ﹢a 2 ＝P。
According to the law of constant volume of plastic deformation, the volume V of the A1 rotator in FIG. 1 1 Volume V of the rotating body which should be equal to A2 2 V, i.e 1 ＝V 2 ，
A1 is an isosceles trapezoid in cross section of a screw tap extruded into a screw groove, and A1 (area): a is that 1 ＝(a 1 ﹢b 1 )/2×(d﹣d 0 )/2. A2 is a cross-section isosceles trapezoid extruded by a tap, A2 (area): (a) 2 ﹢b 2 )/2×(d 0 －d 1 )/2，
a 1 ＝AB＝P/8＝0.125P b 2 ＝FG＝0.25P
d 1 ＝d﹣1.0825P；
V=2pi LA where L is according to Gu Lujin law 2 1 ＝X 1 ﹢d 0 /2，L 2 ＝X 2 ﹢d 1 /2。X 1 、X 2 The distance from the center of the isosceles trapezoid to the bottom edge is the distance, and A is the area of the isosceles trapezoid.
V 1 ＝2π×〔(h 1 /3×(2a 1 ﹢b 1 )/(a 1 ﹢b 1 ))﹢d 0 /2〕×(a 1 ﹢b 1 )
/2×h 1 ..........................................................(1)
Wherein h is 1 ＝(d﹣d 0 )/2，
V 2 ＝2π×〔(h 2 /3×(2a 2 ﹢b 2 )/(a 2 ﹢b 2 ))﹢d 1 /2〕×(a 2 ﹢b 2 )/2
×h 2 Wherein h is 2 ＝(d 0 ﹣d 1 )/2..............................................(2)
V 1 ＝V2；
Solving this equation: d, d 0 ≈d－0.60P。
This function d 0 =d-0.60P is the A1 rotator volume V 1 Complete shift V 2 This displaced volume position state is an ideal state, i.e. V 1 The volume is completely extruded into the cavities of the two prisms, the ideal state torque is maximum, and d 0 Is the minimum value of the bottom hole diameter.
And the minor diameter d of the thread 1 There are tolerances, which are carried out in accordance with GB/T197-2018 common thread tolerance and Cooperation, d 1 The tolerance is positive and negative, and d is calculated according to the value of the tolerance zone 0 Corrected d by =d-0.60P 0 ＝d 1 -0.43-0.60) P, nonferrous metal with small value such as aluminum alloy M3.times.0.5, bottom hole diameterAlloy steel 30 CrMnSiA->1Cr18Ni9Ti/>Titanium alloy->The diameter precision of the bottom hole in the production is reserved 2 positions behind the decimal point, namely the percentile, the level of 0.01mm,
example 5 torque of a tap during cold extrusion was reduced by step extrusion.
In the mechanical model t=k(d﹣d 0 ) 2 Analysis was performed.
Torque T and d-d 0 Is square, so in d-d 0 Add d between 3 And let d 3 The pitch of the internal thread of d is the same as that of d, d is added 3 The rear torque formula is:
T＝K(d﹣d 0 ) 2 ＝K(d﹣d 3 ﹢d 3 ﹣d 0 ) 2 ＝K〔(d﹣d 3 )﹢(d 3 ﹣d 0 )〕
2 ＝K(d﹣d 3 ) 2 ﹢K(d 3 ﹣d 0 ) 2 ﹢2K(d﹣d 3 )(d 3 ﹣d 0 )。
let d 0 ＜d 3 ＜d，d﹣d 3 ＞0，d 3 ﹣d 0 > 0, the conclusion is as follows: (1) t=k (d-d) 0 ) 2 ＞K(d﹣d 3 ) 2 ﹢K(d 3 ﹣d 0 ) 2 Similarly (2)K (d-d) 0 ) 2 ＞K(d﹣d 3 ) 2 ，③K(d﹣d 0 ) 2 ＞K(d 3 ﹣d 0 ) 2 。
According to the characteristic of the relation between the torque of the cold extrusion internal thread and the diameter of the bottom hole, combining the conclusion of the mathematical derivation of the steps, dividing one cold extrusion internal thread tap or forming into two times. Because the extrusion times are too many, a plurality of special taps with different diameters and identical screw pitches need to be processed, the processing cost is increased, and the situation that the screw threads are disordered due to the fact that the inner wall of a workpiece is deformed for a plurality of times due to the too many extrusion times is caused, the two-step cold extrusion forming is adopted. The extrusion torque of such a step-forming drops very rapidly because T and (d-d) 0 ) Is a nonlinear function and is a square relationship.
Although a certain residual stress is brought about by the first cold extrusion, the internal thread of M22×1.5 is generally not more than 0.35mm, and the first step extrusion (d 3 ﹣d 0 ) The surface residual stress is relatively reduced, and the depth of the hardening layer is relatively reduced. But the matrix HV, σs is unchanged. Assume that the second torque T2 is fully superimposed on the T1 baseAdding:
T1＝K(d 3 ﹣d 0 ) 2 then t2=t1+k (d-d) 3 ) 2 ＝K(d 3 ﹣d 0 ) 2 ﹢K(d﹣d 3 ) 2 ＜K(d﹣d 0 ) 2 I.e. less than the one cold extrusion internal thread forming torque.
And residual stress, case hardening due to d 3 ＞d 0 ，(d 3 ﹣d 0 )＜(d﹣d 0 ) Naturally, it is smaller and shallower than the primary forming, i.e. the second superimposed torque on the first T1 must be less than the primary forming torque. However, after cold extrusion internal thread forming, the residual stress of the 2 nd step extrusion is larger than that of the first step extrusion, and the work hardening is increased. While an increase in the lamination stress of the thread form will necessarily increase its fatigue life.
As shown in table 3, a primary cold extrusion internal thread forming experiment and a step-by-step secondary cold extrusion internal thread forming experiment were performed on high hardness of high temperature alloy and stainless steel, and SKS tapping dedicated oil was used for lubricating oil. The resulting tooth form is shown in fig. 9.
TABLE 3 M3×0.5 Cold extrusion test
Table 3 test data demonstrates that the step extrusion internal thread forming torque is less than the one-shot extrusion internal thread forming torque.
Example 6 the displaced volume relationship of each step in a step extrusion process was determined with energy conservation.
Torque T and (d-d) 0 ) Further theoretical analysis of functional relationship, functional relationship V of metal displacement volume of inner wall of workpiece 1 ＝f(x)＝ax 3 +bx 2 +cx
X＝d﹣d 0 For the internal thread d of the workpiece, the internal thread d is determined by the design drawingUnchanged, then d 0 Increase X and decrease d 0 Decreasing X increases.
Demonstration of conservation of energy, T and (d-d) 0 ) The plastic deformation process is regarded as an adiabatic process, and the work (or power) performed by the external force is equal to the sum of the increase in the internal energy of the object and the total work (or power) required for the metal deformation.
If the kinetic energy is K and the internal energy is U, then at the transition from one state to the other state within a small time δt, the total energy is changed to δk+δu=δa+δq according to the first law of thermodynamics,
in which δA is the volumetric force F i With area force P i Work performed, δq, is the heat dissipated by the object to the surrounding medium.
The change formula of the external force work is δa= ≡ V [F i δu i ﹢(σ ij,j δu i ﹢σ ij δu i , j )]dV is closely related to V and the like, and is the integral of the volume, and the change of the volume influences the work of external force.
The extrusion internal thread is subjected to torque work, and the extrusion internal thread TdQ =δa and dQ is twisted in degrees and radians.
When the torque rotates once, dq=2pi, forming a pitch.
T＝1/2π∫ V [F i δu i ﹢(σ ij,j δu i ﹢σ ij δu i,j )]dV..........(1)
Let v=v 1 ﹢V 2 The additive properties are integrated as determined.
T＝1/2π∫ V [F i δu i ﹢(σ ij,j δu i ﹢σ ij δu i,j )]dV＝1/2π∫ V1 [F i δu i ﹢(σ ij,j δu i ﹢σ ij δu i,j )]dV(T 1 )﹢1/2π∫ V2 [F i δu i ﹢(σ ij,j δu i ﹢σ ij δu i,j )]dV(T 2 ).......(2)
I.e. t=t 1 ﹢T 2 Due to T 1 ﹥0，T 2 Is greater than 0, so T 1 ﹤T,T 2 And < T. It is stated that each step extrusion torque in the step extrusion is smaller than the forming extrusion torque only once.
δu i Small displacement δu i And d 0 (d-d) 0 ) Related to the following. Although the displacement of the particles in the deformed body is difficult to describe accurately δu i Can qualitatively know delta u i ＝f(d﹣d 0 )。
From δa volume integral, t=f (d-d) is known qualitatively 0 )＝a(d﹣d 0 ) 4 ﹢b(d﹣d 0 ) 3 ﹢C(d﹣d 0 ) 2 a.b.c＞0。 (3)
From equation (3), it can be known that and t=k (d-d) 0 ) y The function is equivalent (the corresponding function value of a, b, c, K can be found), K is related to workpiece materials, tap structures, friction coefficients and the like, and the value range of y is 2-4. Table 1: t= 397.1 × (22-d) 0 ) 2.28 Table 2: t=39.8× (8-d) 0 ) 3.35 . Further explanation verifies that y=2 to 4.
Since y=2 to 4, we are with t=k (d-d 0 ) 2 The torque of the internal thread of the step extrusion is required to be smaller than that of the internal thread of the single extrusion, the effect is obvious, and the theoretical analysis is correct. The actual y=2 to 4 effects are self-evident (more pronounced than t=k (d-d) 0 ) 2 ) The practicability is stronger. The test data of table 3 demonstrate this.
By displacement volume calculation, the first displacement volume (64-75%) V1 is d 3 D-d (0.1-0.15) P, (d 3 is the same as d pitch) first internal thread extrusion d 3 The larger value is taken, so that the secondary extrusion tap can smoothly enter the first reserved tooth type threaded hole, the messy buckling and the messy teeth cannot be caused, the diameter precision error of the bottom hole machined by the drill bit can be eliminated and reduced, the roughness is reduced, and the secondary fine drilling supplement machining (step drilling method) is not needed. The stepped tapping method can further improve the surface precision, reduce the roughness, retain the residual stress and the hardening layer, improve the fatigue strength and the service life of the product, simultaneously, d0 can take a relatively smaller value, can also be realized,this increases the tooth height and further improves the mechanical properties. The first extrusion process can replace the fine drilling process, and the cost is not increased.
In the embodiment 7, as shown in fig. 5 and 6, the combined tap of the invention can extrude the through hole thread twice without replacing the tap, the tap is formed by sequentially connecting a positioning section 5, a small diameter section 1, a transition section 2, a standard section 3 and a clamping handle, during processing, the positioning section 5 is in butt joint with a workpiece bottom hole, the tap gradually enters the bottom hole after rotating, the first extrusion is carried out on the inner wall of the workpiece through the edge teeth on the small diameter section 1, the lower-tooth-height-rate thread is formed on the inner wall of the workpiece, then the transition section 2 and the small diameter section 1 are in prefabricated threaded connection, the inner wall of the workpiece is gradually extruded by the standard section 3, residual stress is generated by the lower-tooth-height thread formed by the first extrusion, the standard section 3 continues extruding the thread surface on the basis, the hardened layer is deepened, and the surface precision and the thread integrity are increased.
The clamping handle of fig. 5 is thick handle, can adapt to bigger moment of torsion, is fit for the processing of high strength screw thread, and the clamping handle of fig. 6 is thin handle, has also reduced extrusion internal thread moment of torsion, is fit for many internal thread through-hole continuous extrusion processing, has improved efficiency.
Claims (10)
1. An internal thread step-by-step cold extrusion process comprises the following steps:
s1, calculating a functional relation between the diameter of a bottom hole of a workpiece and the nominal diameter and the screw pitch of an internal thread of the workpiece;
in the process of extruding the workpiece by the screw tap, the volume V of the thread metal extruded by the screw tap 2 Volume V of thread groove produced by extruding screw tap extrusion edge tooth into inner wall of workpiece 1 The values of the two are equal to each other,
V 1 ＝V 2 (1)，
V 1 ＝2π×〔(h 1 /3×(2a 1 ﹢b 1 )/(a 1 ﹢b 1 ))﹢d 0 /2〕×(a 1 ﹢b 1 )/2×h 1 (2)，
V 2 ＝2π×〔(h 2 /3×(2a 2 ﹢b 2 )/(a 2 ﹢b 2 ))﹢d 1 /2〕×(a 2 ﹢b 2 )/2×h 2 (3)，
a 1＝ 0.125P (4)，
b 1 ＝0.125P﹢0.5774(d﹣d 0 ) (5)，
a 2 ＝0.875P﹣0.5774(d﹣d 0 ) (6)，
b 2 ＝0.25P (7)，
h 1 ＝(d﹣d 0 )/2 (8)，
h 2 ＝(d 0 ﹣d 1 )/2 (9)，
d 1 ＝d﹣1.0825P (10)，
b 1 ﹢a 2 ＝P (11)，
bringing formulae (2) - (11) into formula (1) to give d 0 ≈d-0.60P；
S2, correcting the diameter d of the bottom hole according to the numerical value of the thread tolerance zone 0 ＝d﹣(0.43～0.60)P，
Wherein a is 1 Is the width of the thread crest of the thread groove, b 2 Crest width, h, of thread extruded for tap 1 Depth of screw tap into thread groove, h 2 The thread height of the extrusion thread for the tap, P is the pitch of the internal thread, d 1 The diameter of the thread is small, and d is the nominal diameter of the internal thread of the workpiece;
s3, selecting the diameter of the bottom hole according to the workpiece material and then machining the bottom hole;
s4, performing cold extrusion processing on the internal threads of the workpiece step by using the screw tap.
2. The internal thread step-wise cold extrusion process of claim 1, wherein: the step S4 specifically includes:
s41, performing primary cold extrusion on the internal thread of the workpiece by using a small-diameter tap with the diameter smaller than the nominal diameter of the internal thread of the workpiece and the screw pitch identical to that of the internal thread of the workpiece, so that the displacement volume of the metal on the inner wall of the workpiece is a complete internal thread displacement volume V 1 64% -75% of the total weight of the steel sheet;
s42, performing one-time cold extrusion by using a standard tap with the diameter equal to the nominal diameter of the internal thread of the workpiece and the screw pitch identical to that of the internal thread of the workpiece to obtain the complete internal thread.
3. The internal thread step-wise cold extrusion process of claim 2, wherein: the rotating speed of the machine tool in the steps S41 and S42 is 25r/min, and cold extrusion special oil is used in the extrusion process.
4. The internal thread step-wise cold extrusion process of claim 2, wherein: the diameter of the small-diameter tap in the step S41 is calculated by the following method:
V 3 ＝(64％～75％)V 1 (12)，
V 3 ＝2π×〔(h 3 /3×(2a 3 ﹢b 3 )/(a 3 ﹢b 3 ))﹢d 0 /2〕×(a 3 ﹢b 3 )/2×h 3 (13)，
h 3 ＝(d 3 ﹣d 0 )/2 (14)，
a 3 ＝0.125P (15)，
b 3 ＝0.125P﹢0.5774(d 3 ﹣d 0 ) (16)，
carrying out the following formulas (2), (13) to (16) into formula (12):
d 3 ＝d－(0.1～0.15)P；
V 3 a is the volume of the small diameter tap extruded into the thread groove 3 The crest width h of the thread groove is extruded into the tap with small diameter 3 D, the depth of the small-diameter tap extruded into the thread groove 3 Is the nominal diameter of the small diameter tap.
5. The internal thread step-wise cold extrusion process of claim 2, wherein: and if the bottom hole of the workpiece is a through hole, carrying out one-step combined machining by using a combined tap.
6. The internal thread step-wise cold extrusion process of claim 5, wherein: the combined tap comprises a small-diameter section (1) and a standard section (3), the small-diameter section (1) and the standard section (3) are connected smoothly through a transition section (2), the other end of the small-diameter section (1) is connected smoothly with a positioning head (5), and the other end of the standard section (3) is connected with a clamping handle (4).
7. The internal thread step-by-step cold extrusion process of claim 6, wherein: the diameter relation between the small diameter section (1) and the standard section (3) is d Small size ＝d Label (C) ﹣(0.1～0.15)P。
8. The internal thread step-by-step cold extrusion process of claim 6, wherein: the clamping handle (4) is a thick handle or a thin handle.
9. The internal thread step-wise cold extrusion process of claim 8, wherein: the diameter of the clamping handle (4) of the thick handle is larger than that of the standard section (3), and the clamping handle (4) is smoothly connected with the standard section (3).
10. The internal thread step-wise cold extrusion process of claim 8, wherein: the diameter of the clamping handle (4) of the thin handle is smaller than that of the standard section (3).
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| JP2000266024A (en) * | 1999-03-16 | 2000-09-26 | Niigata Eng Co Ltd | Method of working female thread part |
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| JP2007125680A (en) * | 2005-11-07 | 2007-05-24 | Asahi Tec Corp | Method for manufacturing plated female screw and screw tap |
| CN103464842A (en) * | 2013-08-23 | 2013-12-25 | 西安交通大学 | Internal thread vibration and extrusion tapping process |
| CN109604488A (en) * | 2018-12-21 | 2019-04-12 | 哈尔滨理工大学 | A kind of extruding method of magnesium alloy AZ31 internal screw thread |
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Patent Citations (5)
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| JP2000266024A (en) * | 1999-03-16 | 2000-09-26 | Niigata Eng Co Ltd | Method of working female thread part |
| JP2007125680A (en) * | 2005-11-07 | 2007-05-24 | Asahi Tec Corp | Method for manufacturing plated female screw and screw tap |
| CN1883875A (en) * | 2006-07-05 | 2006-12-27 | 潍柴动力股份有限公司 | Method for processing screw hole in connecting rod body of Steyr diesel engine and dedicated extruded tap therefor |
| CN103464842A (en) * | 2013-08-23 | 2013-12-25 | 西安交通大学 | Internal thread vibration and extrusion tapping process |
| CN109604488A (en) * | 2018-12-21 | 2019-04-12 | 哈尔滨理工大学 | A kind of extruding method of magnesium alloy AZ31 internal screw thread |
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